Autonomic Nervous System
Autonomic Nervous System
• Regulates the activity of smooth muscle,
cardiac muscle, and certain glands
Autonomic Nervous System
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2.
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Structurally it includes;
Autonomic Sensory neurons
Integrating Centers in the CNS
Autonomic Motor Neurons
Autonomic Nervous System
• Autonomic sensory input is not consciously
perceived
Autonomic Nervous System
• Autonomic motor neurons either increase
(excite) or decrease (inhibit) ongoing
activities of cardiac muscle, smooth
muscle, and glands
Autonomic Nervous System
• The axon of the first motor neuron of the
ANS extends from the CNS and synapses
in a ganglion with the second neuron
Autonomic Nervous System
• The second neuron synapses on an
effector
Autonomic Nervous System
• Parasympathetic and sympathetic
preganglionic fibers release acetylcholine
Autonomic Nervous System
• Parasympathetic postganglionic fibers
release acetylcholine
Autonomic Nervous System
• Sympathetic postganglionic fibers usually
release norepinephrine
Autonomic Nervous System
• The output part of the ANS is divided
into;
1. Sympathetic
2. Parasympathetic
Anatomy Of The Autonomic Motor
Pathway
• Preganglionic neuron – The first of two
autonomic motor neurons is called a
preganglionic neuron
Preganglionic Neuron
• Its cell body is in the brain or spinal cord
Preganglionic Neuron
• Its axon is called a preganglionic fiber
which passes out of the CNS as part of a
cranial or spinal nerve
Preganglionic Neuron
• The preganglionic fiber separates from the
nerve and synapses with the
postganglionic neuron and excites it by
releasing ACh
Preganglionic Neuron
• The cell bodies of sympathetic
preganglionic neurons are in the lateral
gray horns of the 12 thoracic and the first
2 to 3 lumbar segments
Preganglionic Neurons
• The cell bodies of parasympathetic
preganglionic neurons are in cranial nerve
nuclei (III, VII, IX, X) in the brain stem
and lateral gray horns of the 2nd through
4th sacral segments of the cord
Postganglionic Neuron
• Its cell body and dendrites are located in
an autonomic ganglion
Postganglionic Neuron
• Postganglionic fiber – the axon of a
postganglionic neuron which terminates in
an effector such as the heart
Postganglionic Neuron
• Parasympathetic preganglionic neurons
synapse with postganglionic neurons in
terminal ganglia
Postganglionic Neuron
• Parasympathetic postganglionic fibers
release acetylcholine
Postganglionic Neuron
• Sympathetic preganglionic neurons
synapse with postganglionic neurons in
sympathetic ganglia
Postganglionic Neurons
• Sympathetic postganglionic fibers usually
release norepinephrine
Cholinergic Neurons
• Releases the neurotransmitter ACh
Cholinergic Neurons
Include;
1. Sympathetic and Parasympathetic
preganglionic neurons
2. Parasympathetic postganglionic neurons
3. Sympathetic postganglionic neurons that
innervate sweat glands and arteries to
skeletal muscle
Cholinergic Receptors
Two types;
1. Nicotinic
2. Muscarinic
Cholinergic Receptors
• Activation of nicotine receptors causes
excitation of the postsynaptic cell
Cholinergic Receptors
• Activation of muscarine receptors can
cause either excitation or inhibition
depending on the cell that bears the
receptors
Cholinergic Receptors
• Nicotinic Ach receptors are on skeletal
muscle and the dendrites of
postganglionic neurons
Cholinergic Receptors
• Muscarinic Ach receptors are on target
organs (heart)
Andrenergic Neurons
• Release Norepinephrine
• Usually sympathetic postganglionic
neurons
Andrenergic Receptors
Two Types;
1. Alpha
2. Beta
Andrenergic Receptors
Subtypes;
1. Alpha 1
2. Alpha 2
3. Beta 1
4. Beta 2
5. Beta 3
Andrenergic Receptors
Depending on the subtype activation of the
receptor can result in either excitation or
inhibition
Andrenergic Neurons
Effects of Adrenergic neurons are longer
lasting than those triggered by cholinergic
neurons